Many companies are struggling to develop new wireless Internet technologies which can be used to provide various communication services, such as wireless Internet services, regardless of places. Wireless Internet refers to an environment or technology which allows a moving user to access the Internet through a wireless network. With the development of mobile communication technologies and the explosive increase in the use of mobile phones, the wireless Internet services have also been greatly developed.
Among a variety of wireless Internet services provided to mobile terminals, such as cellular phones, PDAs or notebook computers, LBS is being popularized more and more due to its wide applications and availability. The LBS can be used in various applications and conditions, such as emergency assistance, criminal tracking, GIS (Geographic Information System), difference of mobile communication fees according to locations, traffic information, vehicle navigation, logistics control and location-based CRM (Customer Relationship Management).
In order to exploit the LBS, it is required to identify the location of a mobile communication terminal. A GPS is generally used to track the location of a mobile communication terminal.
The GPS is a worldwide navigation and positioning system which determines the location of an object on earth by using 24 GPS satellites orbiting the earth at an altitude of approximately 20,000 km. The GPS uses radio waves in a bandwidth of 1.5 GHz. Ground control stations which monitor the GPS satellites receive information transmitted from the satellites and synchronize transmission time. Users can monitor their locations by using GPS receivers. Generally, the GPS determines the location of an object by triangulation by using four satellites. Three satellites are used for accurate triangulation, and a fourth satellite is in orbit to correct a timing error.
However, it is difficult to determine the location of an object in downtown areas surrounded by high-rise buildings due to so-called multi-path effects and the lack of visible satellites. Also, an accurate location determination can hardly be made in a tunnel or in a basement of a building where satellites are not visible (where radio waves cannot reach). In addition, GPS receivers may require a TTFF (Time To First Fix) of several minutes to over ten minutes to initially determine their location, thereby causing inconvenience to the users of location-based wireless Internet services.
A-GPS answers some of the inherent problems with GPS. The A-GPS determines the location of a mobile communication terminal by combining GPS with wireless communication network resources. A mobile communication terminal collects geolocation information from both the GPS satellites and a wireless communication network to determine its location in 3-D in geodetic coordinates (latitude, longitude and altitude) with high accuracy. The wireless network and the mobile communication terminal transmit and receive data or messages by using parameters defined in IS (Interim Standard)-801-1.
In a CDMA (Code Division Multiple Access) communication network, one wireless base station (BS) covers an area corresponding to its maximum antenna range (MAR) . The MAR is an area having a radius equal to the maximum distance that radio waves emitted from a base station antenna reach.
However, it is costly to install base stations based on MAR to cover every area in a country. Base stations installed in current mobile communication networks are set to have a uniform MAR of 3 Km to 5 Km. To provide high quality location-based services in the current mobile communication networks, base stations should be installed at every MAR coverage area.
To reduce the cost of installing base stations, the current mobile communication networks broaden the coverage of a voice or data call of a wireless base station by installing at least one optical repeater connected to the wireless base station by an optical cable. The optical repeater uses the same identification code as the wireless base station to which it is connected. Accordingly, the optical repeater can transfer the identification code of the connected base station to a position determination entity when a mobile communication terminal is located within an area covered by the optical repeater.
Therefore, if the terminal is in an area covered by the optical repeater, it is difficult to determine the location of a mobile communication terminal by using an A-GPS scheme. In the A-GPS scheme, a mobile communication terminal is not equipped with a GPS receiver. The mobile communication terminal obtains an identification code (address) of the wireless base station covering the area in which it is located, and transfers the identification code to the position determination entity through a mobile communication network. The position determination entity confirms the identification code received through the mobile communication network and detects an MAR set for the pertinent wireless base station.
Based on the detected MAR, the position determination entity extracts coordinate information of GPS satellites from which GPS signals can be received in the coverage area of the wireless base station. Subsequently, the position determination entity transfers the coordinate information as assistance data to the mobile communication terminal through the mobile communication network. Upon receiving the assistance data, the mobile communication terminal detects the GPS signals based on the coordinate information of the GPS satellites which is included in the assistance data.
The coordinate information of the GPS satellites, which is received by the mobile communication terminal under the A-GPS scheme, can effectively be used only when the mobile communication terminal is located within the area corresponding to the MAR set for the wireless base station. If the mobile communication terminal is located at the boundary of the base station or in an area covered by an optical repeater that uses the same identification code as the base station, the assistance data will be improper and useless. If the mobile communication terminal detects GPS signals by using improper GPS coordinate information, it will fail to accurately determine its location.